Method of manufacturing a semiconductor structure having stacked semiconductor devices

ABSTRACT

A semiconductor structure includes flip chips or other semiconductor devices that are mounted on printed circuit boards. The printed circuit boards are stacked to increase the circuit density of the semiconductor structure. The printed circuit boards include cavities or openings to accommodate the flip chips or semiconductor devices and thus reduce the overall size of the semiconductor structure. The flip chips or semiconductor devices from adjacent printed circuit boards may extend into the cavities or openings or simply occupy the cavities or openings from the same printed circuit board.

CROSS-REFERENCE TO RELATED APPLICATION

This is a divisional application of co-pending application Ser. No.09/141,690 filed on Aug. 28, 1998 by Akram et al. now U.S. Pat. No.6,313,522, entitled SEMICONDUCTOR STRUCTURE HAVING STACKED SEMICONDUCTORDEVICES.

BACKGROUND OF THE INVENTION

The present invention relates in general to an apparatus and method forincreasing semiconductor device density, and more particularly, toarranging semiconductor devices within and over substrates to achievedensely packaged semiconductor structures.

Chip On Board techniques are used to attach semiconductor dice to aprinted circuit board, including flip chip attachment, wirebonding, andtape automated bonding (TAB). Flip chip attachment consists of attachinga flip chip to a printed circuit board or other substrate. A flip chipis a semiconductor chip that has a pattern or array of electricalterminations or bond pads spaced around an active surface of the flipchip for face down mounting of the flip chip to a substrate. Generally,the flip chip has an active surface having Ball Grid Array (BGA) or PINGrid Array (PGA) electrical connectors. The BGA comprises an array ofminute solder balls disposed on the surface of the flip chip thatattaches to the substrate (the attachment surface). The PGA comprises anarray of small pins that extend substantially perpendicular from theattachment surface of the flip chip. The pins conform to a specificarrangement on a printed circuit board or other substrate for attachmentthereto.

With the BGA, the solder or other conductive ball arrangement on theflip chip must be a mirror-image of the connecting bond pads on theprinted circuit board such that precise connection is made. The flipchip is bonded to the printed circuit board by refluxing the solderballs. The solder balls may also be replaced with a conductive polymer.With the PGA, the pin arrangement of the flip chip must be amirror-image of the pin recesses on the printed circuit board. Afterinsertion, the flip chip is generally bonded by soldering the pins intoplace. An under-fill encapsulant is generally disposed between the flipchip and the printed circuit board for environmental protection and toenhance the attachment of the flip chip to the printed circuit board.

Wirebonding attachment generally begins with attaching a semiconductorchip to the surface of a printed circuit board with an appropriateadhesive, such as an epoxy. In wirebonding, bond wires are attached, oneat a time, to each bond pad on the semiconductor chip and extend to acorresponding lead, trace end or bond pad on the printed circuit board.The bond wires are generally attached using industry-standardwirebonding techniques, such as ultrasonic bonding, thermocompressionbonding or thermosonic bonding. Ultrasonic bonding comprises thecombination of pressure and ultrasonic vibration bursts to form ametallurgical cold weld. Thermocompression bonding comprises thecombination of pressure and elevated temperature to form a weld.Thermosonic bonding comprises the combination of pressure, elevatedtemperature, and ultrasonic vibration bursts to form a weld. Thesemiconductor chip may be oriented either face up or face down (with itsactive surface and bond pads either up or down with respect to thecircuit board) for wire bonding, although face up orientation is morecommon. With TAB, ends of metal leads carried on an insulating tape,such as a polyamide, are respectively attached to the bond pads on thesemiconductor chip and to the lead or trace ends on the printed circuitboard. An encapsulant is generally used to cover the bond wires and themetal tape leads to prevent contamination.

Higher performance, lower cost, increased miniaturization of components,and greater packaging density of integrated circuits are ongoing goalsof the computer industry. As new generations of integrated circuitproducts are released, the number of devices used to fabricate themtends to decrease due to advances in technology even though thefunctionality of these products increases. For example, on the average,there is approximately a 10 percent decrease in components for everyproduct generation over the previous generation with equivalentfunctionality.

In integrated circuit packaging, in addition to component reduction,surface mount technology has demonstrated an increase in semiconductorchip density on a single substrate or board despite the reduction of thenumber of components. This results in more compact designs and formfactors, and significant increase in integrated circuit density.However, greater integrated circuit density is primarily limited by thespace or “real estate” available for mounting dice on a substrate, suchas a printed circuit board.

One method of further increasing integrated circuit density is to stacksemiconductor dice vertically. U.S. Pat. No. 5,012,323 issued Apr. 30,1991 to Farnworth teaches combining a pair of dice mounted on opposingsides of a lead frame. An upper, smaller die is back-bonded to the uppersurface of the leads of the lead frame via a first adhesively coated,insulated film layer. A lower, larger die is face-bonded to the lowerlead frame die-bonding region via a second, adhesively coated,insulative, film layer. The wirebonding pads on both upper die and lowerdie are interconnected with gold or aluminum bond wires to the ends oftheir associated lead extensions. The lower die must be slightly largerthan the upper die so that the die pads are accessible from abovethrough a bonding window in the lead frame to allow the gold wireconnections to be made to the lead extensions. This arrangement has amajor disadvantage from a production standpoint as the same size diecannot be used.

U.S. Pat. No. 5,291,061 issued Mar. 1, 1994 to Ball teaches a multiplestacked dice device containing up to four stacked dice supported on adie-attach paddle of a lead frame. The assembly does not exceed theheight of current single die packages and the bond pads of each die arewirebonded to lead fingers. The low profile of the device is achieved byclose-tolerance stacking which is made possible by a low-loop-profilewirebonding operation and thin adhesive layers between the stacked dice.However, Ball requires long bond wires to electrically connect thestacked dice to the lead frame. These long bond wires increaseresistance and may result in bond wire sweep during encapsulation. Also,Ball requires the use of spacers between the dice.

U.S. Pat. No. 5,323,060 issued Jun. 21, 1994 to Fogal et al. (Fogal)teaches a multichip module that contains stacked die devices. Theterminals or bond pads of die devices are wirebonded to a substrate orto adjacent die devices. However, as discussed with Ball, Fogal requireslong bond wires to electrically connect the stacked dice bond pads tothe substrate. Fogal also require the use of spacers between the die.

U.S. Pat. Nos. 5,422,435 and 5,495,398 to Takiar et al. (Takiar) teachstacked dice having bond wires extending to each other and to the leadsof a carrier member such as a lead frame. Takiar also has the problem oflong bond wires, as well as, requiring specific sized or custom designeddice to achieve a proper stacked combination.

U.S. Pat. No. 5,434,745 issued Jul. 18, 1995 to Shokrgozar et al.(Shokrgozar) discloses a stackable packaging module comprising astandard die attached to a substrate with a spacer frame placed on thesubstrate to surround the die. The substrate/die/spacer combinations arestacked one atop another to form a stacked assembly. The outer edge ofthe spacer frame has grooves in which a conductive epoxy is disposed.The conductive epoxy forms electric communication between the stackedlayers and/or to the final substrate to which the stacked assembly isattached. However, Shokrgozar requires specialized spacer frames and asubstantial number of assembly steps, both of which increase the cost ofthe final assembly.

U.S. Pat. No. 5,128,831 issued Jul. 7, 1992 to Fox, III et al. (Fox)also teaches a standard die attached to a substrate with a spacer frameplaced on the substrate to surround the die. The stacked layers and/orthe final substrate are in electric communication with conductive epoxyextending through the spacer frames. However, Fox also requiresspecialized spacer frames, numerous assembly steps, and is limited inits flexibility to utilize a variety of dice.

Another prior art stacking arrangement is shown in FIG. 1. A pluralityof printed circuit boards 10 are stacked on top of each other and on topof a motherboard 12. Each of the printed circuit boards 10 include asemiconductor die 14 mounted to a top surface of each respective printedcircuit board 10 using methods known in the art. Bond pads on each dieare electrically coupled to each respective printed circuit board 10.The printed circuit boards 10 and the motherboard 12 are electricallyand physically coupled together using solder balls 16. It should beapparent that the solder balls 16 must be sufficiently thick so that theprinted circuit boards 10 do not contact or interfere with adjacent dies14. The thick solder balls 16 increase the overall size of the structureand the length of the signal paths.

Accordingly, there is an ongoing need for semiconductor structureshaving increased circuit density. There is a further need forsemiconductor structures in which printed circuit boards are stacked toincrease circuit density. There is a still further ongoing need forsemiconductor structures having shorter signal paths. Preferably, suchsemiconductor structures are relatively inexpensive, easy tomanufacture, and use standard die configurations and components.

SUMMARY OF THE INVENTION

The present invention meets these needs by providing a semiconductorstructure in which flip chips or other semiconductor devices are mountedon printed circuit boards. The printed circuit boards are stacked toincrease the circuit density of the semiconductor structure. The printedcircuit boards include cavities or openings to accommodate the flipchips or semiconductor devices and thus reduce the overall size of thesemiconductor structure. The flip chips or semiconductor devices fromadjacent printed circuit boards may extend into the cavities or openingsor simply occupy the cavities or openings from the same printed circuitboard.

According to a first aspect of the present invention, a semiconductorstructure comprises a base substrate, a first substrate and at least onesemiconductor. The base substrate comprises a first surface having afirst plurality of base substrate bond pads formed thereon. The firstsubstrate comprises a first surface, a second surface and at least onecavity formed therein. One of the first and second surfaces includes afirst plurality of first substrate bond pads. At least one of the firstplurality of first substrate bond pads is electrically coupled to atleast one of the first plurality of base substrate bond pads. Thesemiconductor device includes a plurality of semiconductor device bondpads. The semiconductor device is positioned generally within the cavityof the first substrate between the base substrate and the firstsubstrate with at least one of the plurality of semiconductor devicebond pads electrically coupled to at least one of the first plurality ofbase substrate bond pads.

The other of the first and second surfaces of the first substrate maycomprise a second plurality of first substrate bond pads while thesemiconductor structure may further comprise a second semiconductordevice having a plurality of second semiconductor device bond pads. Atleast one of the plurality of second semiconductor device bond pads iselectrically coupled to at least one of the second plurality of firstsubstrate bond pads. A center of the at least one semiconductor deviceand a center of the second semiconductor device may be substantiallyaligned about a line substantially perpendicular to the base substrateand the first substrate.

The semiconductor structure may further comprise a plurality ofsemiconductor devices, each comprising a plurality of bond pads formedthereon. The first substrate may comprise a plurality of cavities witheach of the plurality of semiconductor devices being positioned withinrespective ones of the plurality of cavities and at least one of theplurality of bond pads of each of the plurality of semiconductor deviceselectrically coupled to respective ones of the plurality of bond pads ofthe base substrate. The semiconductor device may comprise asemiconductor die formed within a semiconductor package. Thesemiconductor package may comprise a package selected from the groupconsisting of a chip-scale package, a ball grid array, a chip-on-board,a direct chip attach, and a flip-chip.

Preferably, the semiconductor device is electrically and physicallycoupled to the base substrate via solder balls coupling at least one ofthe plurality of semiconductor device bond pads to at least one of thefirst plurality of base substrate bond pads. The first substrate ispreferably electrically and physically coupled to the base substrate viasolder balls coupling at least one of the first plurality of firstsubstrate bond pads to at least one of the first plurality of basesubstrate bond pads. The base substrate may further comprise a secondsurface having a second plurality of base substrate bond pads formedthereon. Preferably, at least one of the second plurality of basesubstrate bond pads is electrically coupled to external circuitry. Thebase substrate may further comprise a plurality of base substrate traceleads electrically coupling at least a portion of the first plurality ofbase substrate bond pads to at least a portion of the second pluralityof base substrate bond pads.

According to another aspect of the present invention, a semiconductorstructure comprises a base substrate, a first substrate, a secondsubstrate, a first semiconductor device and a second semiconductordevice. The base substrate includes a first surface having a firstplurality of base substrate bond pads formed thereon and a secondsurface having a second plurality of base substrate bond pads formedthereon. The base substrate further comprises a plurality of basesubstrate trace leads electrically coupling at least a portion of thefirst plurality of base substrate bond pads to at least a portion of thesecond plurality of base substrate bond pads. The first substrateincludes a first surface, a second surface, and at least one cavityformed therein. The first surface of the first substrate comprises afirst plurality of first substrate bond pads formed thereon and thesecond surface of the first substrate comprises a second plurality offirst substrate bond pads formed thereon. The first substrate iselectrically and physically coupled to the base substrate via solderballs coupling at least one of the first plurality of first substratebond pads to at least one of the first plurality of base substrate bondpads. The second substrate includes a first surface, a second surface,and at least one cavity formed therein. The first surface of the secondsubstrate includes a first plurality of second substrate bond padsformed thereon and the second surface of the second substrate comprisesa second plurality of second substrate bond pads formed thereon. Thesecond substrate is electrically and physically coupled to the firstsubstrate via solder balls coupling at least one of the second pluralityof first substrate bond pads to at least one of the first plurality ofsecond substrate bond pads. The first semiconductor device includes aplurality of first semiconductor device bond pads formed thereon. Thefirst semiconductor device is positioned generally within the cavity ofthe first substrate and is physically and electrically coupled to thebase substrate via solder balls coupling at least one of the pluralityof first semiconductor device bond pads to at least one of the firstplurality of base substrate bond pads. The second semiconductor deviceincludes a plurality of second semiconductor device bond pads formedthereon. The second semiconductor device is positioned generally withinthe cavity of the second substrate and is physically and electricallycoupled to the first substrate via solder balls coupling at least one ofthe plurality of second semiconductor device bond pads to at least oneof the second plurality of first substrate bond pads.

According to yet another aspect of the present invention, thesemiconductor structure comprises a base substrate, a first substrateand at least one semiconductor device. The base substrate comprises afirst surface having a first plurality of base bond pads formed thereon.The first substrate includes a first surface, a second surface and atleast one opening formed therein. One of the first and second surfacesincludes a first plurality of first substrate bond pads with at leastone of the first plurality of first substrate bond pads beingelectrically coupled to at least one of the first plurality of substratebase bond pads. The semiconductor device includes a plurality ofsemiconductor device bond pads. The semiconductor device is positionedgenerally within the opening of the first substrate between the basesubstrate and the first substrate with at least one of the plurality ofsemiconductor device bond pads electrically coupled to at least one ofthe first plurality of base substrate bond pads. Preferably, thesemiconductor device is electrically and physically coupled to the basesubstrate via solder balls coupling at least one of the plurality ofsemiconductor device bond pads to at least one of the first plurality ofbase substrate bond pads.

According to a further aspect of the present invention, a semiconductorstructure comprises a first substrate, an interconnect device and atleast one semiconductor device. The first substrate has at least oneopening and a surface including a plurality of first substrate bond padsformed thereon. The interconnect device is positioned over the openingof the first substrate and is coupled thereto. The semiconductor deviceincludes a plurality of semiconductor device bond pads. Thesemiconductor device is positioned generally over the opening of thefirst substrate and is coupled to the interconnect device.

The interconnect device may comprise a plurality of contacts with atleast one of the plurality of contacts being electrically coupled to atleast one the plurality of semiconductor device bond pads. At least oneof the plurality of contacts is preferably electrically coupled to atleast one the plurality of first substrate bond pads.

According to a still further aspect of the present invention, asemiconductor structure comprises a base substrate, a first substrate, afirst semiconductor device and a second semiconductor device. The basesubstrate includes a first surface having a first plurality of base bondpads formed thereon. The first substrate includes a first surface havinga first plurality of first substrate bond pads, a second surface havinga second plurality of first substrate bond pads, and at least oneopening formed therein. At least one of the first plurality of firstsubstrate bond pads is electrically coupled to at least one of the firstplurality of base substrate bond pads. The interconnect device ispositioned over the opening of the first substrate and is coupled to thefirst substrate. The first semiconductor device includes a plurality offirst semiconductor device bond pads. The first semiconductor device ispositioned generally within the opening of the first substrate betweenthe base substrate and the first substrate with at least one of theplurality of first semiconductor device bond pads electrically coupledto at least one of the first plurality of base substrate bond pads. Thesecond semiconductor device includes a plurality of second semiconductordevice bond pads. The second semiconductor device is positionedgenerally over the opening of the first substrate and is coupled to theinterconnect device.

Preferably, the interconnect structure is electrically and physicallycoupled to the second surface of the first substrate. At least one ofthe second semiconductor device bond pads is electrically coupled to thefirst substrate through the interconnect device. The first substrate mayfurther comprise a plurality of first substrate trace leads electricallycoupling at least a portion of the first plurality of first substratebond pads to respective ones of a first plurality of contacts on theinterconnect device. At least one of the second semiconductor devicebond pads may be electrically coupled to the first substrate via a bondwire. The interconnect structure may comprise a flex circuit or TABtape. The semiconductor structure may further comprise a plurality ofthe first substrates, a plurality of the first semiconductor devices anda plurality of interconnect devices.

According to a yet still further aspect of the present invention, asemiconductor structure comprises a base substrate, a first substrate, asecond substrate, a first interconnect device, a second interconnectdevice, a first semiconductor device, a second semiconductor device anda third semiconductor device. The base substrate includes a firstsurface having a first plurality of base substrate bond pads formedthereon and a second surface having a second plurality of base substratebond pads formed thereon. The base substrate further comprises aplurality of base substrate trace leads electrically coupling at least aportion of the first plurality of base substrate bond pads to at least aportion of the second plurality of base substrate bond pads. The firstsubstrate includes a first surface, a second surface and at least oneopening formed therein. The first surface of the first substratecomprises a first plurality of first substrate bond pads formed thereonand the second surface of the first substrate comprises a secondplurality of first substrate bond pads formed thereon. The firstsubstrate is electrically and physically coupled to the base substratevia solder balls coupling at least one of the first plurality of firstsubstrate bond pads to at least one of the first plurality of basesubstrate bond pads. The first substrate further comprises a pluralityof first substrate trace leads electrically coupling at least a portionof the first plurality of first substrate bond pads to at least aportion of the second plurality of first substrate bond pads. The secondsubstrate includes a first surface, a second surface and at least oneopening formed therein. The first surface of the second substratecomprises a first plurality of second substrate bond pads formed thereonand the second surface of the second substrate comprises a secondplurality of second substrate bond pads formed thereon. The secondsubstrate is electrically and physically coupled to the first substratevia solder balls coupling at least one of the first plurality of secondsubstrate bond pads to at least one of the second plurality of firstsubstrate bond pads. The second substrate further comprises a pluralityof second substrate trace leads electrically coupling at least a portionof the first plurality of second substrate bond pads to at least aportion of the second plurality of second substrate bond pads. The firstinterconnect device is positioned over the opening of the firstsubstrate and is physically and electrically coupled to the firstsubstrate. The first interconnect structure comprises a plurality offirst interconnect device contacts. The second interconnect device ispositioned over the at least one opening of the second substrate andphysically and electrically coupled to the second substrate. The secondinterconnect structure also comprises a plurality of second interconnectdevice contacts. The first semiconductor device includes a plurality offirst semiconductor device bond pads. The first semiconductor device ispositioned within the opening of the first substrate between the basesubstrate and the first substrate and is physically and electricallycoupled to the base substrate via solder balls coupling at least one ofthe plurality of first semiconductor device bond pads to at least one ofthe first plurality of base substrate bond pads. The secondsemiconductor device includes a plurality of second semiconductor devicebond pads. The second semiconductor device is positioned within theopening of the second substrate between the first substrate and thesecond substrate and is physically and electrically coupled to the firstinterconnect device via solder balls coupling at least one of theplurality of second semiconductor device bond pads to at least one ofthe plurality of first interconnect device contacts. The thirdsemiconductor device includes a plurality of third semiconductor devicebond pads. The third semiconductor device is physically and electricallycoupled to the second interconnect device via solder balls coupling atleast one of the plurality of third semiconductor device bond pads to atleast one of the plurality of second interconnect device contacts.

According to another aspect of the present invention, a semiconductorstructure comprises a first substrate, an interconnect device and atleast one semiconductor device. The first substrate includes at leastone opening and a surface including a plurality of first substrate bondpads. The interconnect device is positioned over the opening of thefirst substrate and is coupled to the first substrate. The semiconductordevice includes a plurality of semiconductor device bond pads. Thesemiconductor device is positioned generally within the opening of thefirst substrate and is coupled to the interconnect device. Theinterconnect device may be electrically non-conductive. The interconnectdevice may not be electrically coupled to the first substrate such thatat least one of the plurality of semiconductor bond pads is electricallycoupled to at least one of the plurality of first substrate bond padsvia a bond wire. The interconnect device may comprise a flex circuit.

According to yet another aspect of the present invention, asemiconductor structure comprises a base substrate, a first substrate, asecond substrate, a first interconnect device, a second interconnectdevice, a first semiconductor device and a second semiconductor device.The base substrate includes a first surface having a first plurality ofbase substrate bond pads formed thereon. The first substrate includes afirst surface having a first plurality of first substrate bond pads, asecond surface having a second plurality of first substrate bond pads,and at least one opening. At least one of the first plurality of firstsubstrate bond pads is electrically coupled to at least one of the firstplurality of base substrate bond pads. The second substrate includes afirst surface having a first plurality of second substrate bond pads, asecond surface having a second plurality of second substrate bond pads,and at least one opening. At least one of the first plurality of secondsubstrate bond pads is electrically coupled to at least one of thesecond plurality of first substrate bond pads. The first interconnectdevice is positioned over the opening of the first substrate and iscoupled to the first substrate. The second interconnect device ispositioned over the opening of the second substrate and is coupled tothe second substrate. The first semiconductor device includes aplurality of first semiconductor device bond pads. The firstsemiconductor device is positioned generally within the opening of thefirst substrate and is coupled to the first interconnect device. Thesecond semiconductor device includes a plurality of second semiconductordevice bond pads. The second semiconductor device is positionedgenerally within the opening of the second substrate and is coupled tothe second interconnect device.

The first interconnect device may be physically but not electricallycoupled to the first surface of the first substrate. The firstinterconnect device may be physically but not electrically coupled tothe first semiconductor device. At least one of the plurality of firstsemiconductor bond pads is electrically coupled to at least one of thesecond plurality of first substrate bond pads via a bond wire. Theplurality of first semiconductor device bond pads may be positioned on afrontside of the first semiconductor device. A backside of the firstsemiconductor device may be electrically coupled to the firstinterconnect device and at least one of the plurality of firstsemiconductor bond pads may be electrically coupled to at least one ofthe second plurality of first substrate bond pads via a bond wire.

According to yet another aspect of the present invention, a method ofmanufacturing a semiconductor structure comprises providing a basesubstrate having a first surface. A first plurality of base substratebond pads are formed on the first surface of the base substrate. A firstsubstrate is provided having a first surface, a second surface, and atleast one cavity formed within the first surface of the first substrate.A first plurality of first substrate bond pads are formed on the firstsurface of the first substrate. At least one semiconductor device isprovided having a plurality of semiconductor device bond pads. At leastone of the plurality of semiconductor device bond pads is coupled to atleast one of the first plurality of base substrate bond pads. The firstsubstrate is positioned over the first surface of the base substratesuch that the semiconductor device is generally within the cavity of thefirst surface. At least one of the first plurality of first substratebond pads is coupled to at least one of the first plurality of basesubstrate bond pads.

According to a further aspect of the present invention, a method ofmanufacturing a semiconductor structure comprises providing a firstsubstrate having at least one opening. A plurality of first substratebond pads are formed on a surface of the first substrate. Aninterconnect device is provided. The interconnect device is coupled tothe first substrate generally over the opening of the substrate. Atleast one semiconductor device is provided having a plurality ofsemiconductor device bond pads. The semiconductor device is coupled tothe interconnect device generally over the opening of the firstsubstrate.

According to another aspect of the present invention, a method ofmanufacturing a semiconductor structure comprises providing a firstsubstrate having at least one opening. A plurality of first substratebond pads are formed on a surface of the first substrate. Aninterconnect device is provided. The interconnect device is coupled tothe first substrate generally over the opening of the first substrate.At least one semiconductor device is provided having a plurality ofsemiconductor device bond pads. The semiconductor device is coupled tothe interconnect device generally within the opening of the firstsubstrate.

Accordingly, it is an object of the present invention to provide asemiconductor structure having increased circuit density. It is anotherobject of the present invention to provide a semiconductor structurehaving shorter signal paths. Preferably, such semiconductor structuresare relatively inexpensive, easy to manufacture and use standard diesand components. Other features and advantages of the invention will beapparent from the following description, the accompanying drawings andthe appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a prior art stacking arrangement;

FIG. 2 is a cross-sectional view of a stacking arrangement according toa first embodiment of the present invention;

FIGS. 3 and 4 are cross-sectional views of a stacking arrangementaccording to a second embodiment of the present invention; and

FIGS. 5 and 6 are cross-sectional views of a stacking arrangementaccording to a third embodiment of the present invention.

Note: The figures do not include section lines for clarity.Additionally, all figures are illustrative and not drawn to scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 2, a semiconductor structure 10 is illustratedaccording to a first embodiment of the present invention. Thesemiconductor structure 10 comprises a base substrate 12, a firstsubstrate 14, a second substrate 16, a third substrate 18, a firstsemiconductor device 20, a second semiconductor device 22, and a thirdsemiconductor device 24. The semiconductor devices 20, 22, 24 compriseat least one semiconductor die, either in the form of a baresemiconductor die or a semiconductor package. The semiconductor dieitself may be in the form of an integrated circuit, a discretesemiconductor component, e.g., diode, transistor, or any othersemiconductor component having an active semiconductor area. In theillustrated embodiment, the semiconductor devices 20, 22, 24 aresemiconductor packages in the form of flip chips. However, it will beappreciated by those skilled in the art that the semiconductor packagesmay comprise chip-scale packages (CSPs), ball grid arrays (BGAs),chip-on-board (COB), direct chip attach (DCA), and other similarpackages. Regardless of the form, the semiconductor devices 20, 22, 24comprise a plurality of first semiconductor device bond pads 26, aplurality of second semiconductor device bond pads 27, and a pluralityof third semiconductor device bond pads 28, respectively, formed onrespective frontsides 20A, 22A, 24A of the semiconductor devices 20, 22,24. The bond pads 26, 27, 28 may be arranged in a uniform pattern ornon-uniform pattern as required for the particular application. Thebacksides 20B, 22B, 24B of the semiconductor devices 20, 22, 24typically do not include any bond pads but may be electrically biased asis known in the art and as required for the particular application.

The base substrate 12 includes a first surface 12A having a firstplurality of base substrate bond pads 29 formed thereon and a secondsurface 12B having a second plurality of base substrate bond pads 30formed thereon. The base substrate 12 also includes a plurality of basesubstrate trace leads 32, a representative portion being shown in FIG.2. The base substrate trace leads 32 are formed using methods well knownin the art for interconnecting the first plurality of base substratebond pads 28 and the second plurality of base substrate bond pads 30 toeach other and other components, as required for the particularapplication. Accordingly, the base substrate trace leads 32 extendwithin the base substrate 12 and on either or both of the first surface12A and the second surface 12B for connection with other components. Thesecond plurality of base substrate bond pads 30 are configured tointerface and communicate with external circuitry, such as a processor,a bus or other base substrates. In the illustrated embodiment, the basesubstrate 12 is a printed circuit board functioning as a motherboard.However, it will be appreciated by those skilled in the art that thebase substrate 12 may comprise other carriers for the mounting ofsemiconductor devices and electronic components. The bond pads 29, 30may be arranged in a uniform pattern or non-uniform pattern as requiredfor the particular application.

The first, second and third substrates 14, 16, 18 each include a firstsurface 14A, 16A, 18A having a first plurality of substrate bond pads34, 38, 40 formed respectively thereon, a second surface 14B, 16B, 18Bhaving a second plurality of substrate bond pads 40, 42, 44 formedrespectively thereon, and a cavity 14C, 16C, 18C formed respectivelytherein. The bond pads 40, 42, 44 may be arranged in a uniform patternor non-uniform pattern as required for the particular application. Thecavities 14C, 16C, 18C may be formed as the substrates 14, 16, 18 arefabricated, e.g., formed as part of the substrate mold, or machined intothe substrates after the substrates are fabricated. The substrates 14,16, 18 also each include a plurality of substrate trace leads 41, 43,45, representative portions being shown in FIG. 2. The trace leads 41,43, 45 are formed using methods well known in the art forinterconnecting the respective first plurality of substrate bond pads34, 36, 38 and the respective second plurality of substrate bond pads42, 44, 46 to each other and other components, as required for theparticular application. Accordingly, the trace leads 41, 43, 45 extendwithin each respective substrate 14, 16, 18 and on either or both of thefirst surface 14A, 16A, 18A and the second surface 14B, 16B, 18B forconnection with other components. In the illustrated embodiment, thesubstrates 14, 16, 18 comprise printed circuit boards. However, it willbe appreciated by those skilled in the art that the substrates 14, 16,18 may comprise other carriers for the mounting of semiconductor devicesand electronic components.

The first semiconductor device 20 and the first substrate 14 are mountedon the first surface 12A of the base substrate 12 using a plurality ofsolder balls 48. Accordingly, the base substrate bond pads 29, the firstsemiconductor bond pads 26 and the first substrate bond pads 36 arepreferably positioned so that each respective bond pad pair is alignedperpendicularly. The solder balls 48 are positioned betweencorresponding pairs of bond pads 26, 29 and 36, 29 so that the firstsemiconductor device 20 and the first substrate 14 are electrically andphysically coupled to the base substrate 12. The first substrate 14 ispositioned so that the first semiconductor device 20 is positionedwithin the cavity 14C. As the first semiconductor device 20 ispositioned within the cavity 14C, the relative height of thesemiconductor device/substrate stack is relatively small. Further, thethickness of the solder balls 48 is reduced compared to a stack in whichthe substrate must extend completely over the semiconductor device. Thesecond semiconductor device 22 and the second substrate 16 are similarlymounted on the second surface 14B of the first substrate 14 using aplurality of solder balls 49 while the third semiconductor device 24 andthe third substrate 18 are mounted on the second surface 16B of thesecond substrate 16 using a plurality of solder balls 50. It should beapparent the signal length between successive semiconductor devices isreduced compared to the prior art as the signals from the base substrate12 pass through one less substrate for each semiconductor device.

Referring now to FIGS. 3 and 4, with like reference numeralscorresponding to like elements, the semiconductor structure 10 is shownaccording to a second embodiment of the present invention. In thisembodiment, the cavities 14A, 16A, 18A are replaced with openings 14D,16D, 18D extending completely through each respective substrate 14, 16,18. The semiconductor structure 10 also includes a first interconnectdevice 51 and a second interconnect device 52. In the illustratedembodiment of FIG. 3, the interconnect devices 51, 52 are conventionalflex circuits known in the art. A flex circuit generally includes aplurality of wires or traces encapsulated in polyimide. As the namesuggests, a flex circuit is flexible and may bend without damaging thewires. In the illustrated embodiment of FIG. 4, the interconnect devices51, 52 comprise conventional TAB tape. TAB tape is similar to a flexcircuit except it includes conductive bumps 51A, 52A for interfacingwith bond pads on semiconductor devices. Connection is made through acombination of heat and pressure. Whether the interconnect devices 51,52 are flex circuits, TAB tape or other similar interconnect devices,the wires in the interconnect devices 51, 52 terminate in a plurality ofcontacts 54, 56, respectively, for interfacing with bond pads or othersimilar interfaces. For TAB tape, a portion of the contacts 54, 56,include the conductive bumps 51A, 52A described above.

The first interconnect device 51 is mounted to the second surface 14B ofthe first substrate 14 generally over the opening 14D. The firstinterconnect device 51 is mounted to the first substrate 14 usingmethods known in the art to electrically and physically couple a portionof the contacts 54 to corresponding bond pads 42 on the second surface14B of the first substrate 14. It will be appreciated by those skilledin the art that the interconnect device 51 may be physically secured tothe first substrate 14 using an appropriate adhesive, in place of or inaddition to the physical coupling provided by the contacts 54 and thebond pads 42. The second semiconductor device 22 is coupled to the firstinterconnect device 50 using the solder balls 49 to electrically andphysically couple the second semiconductor device bond pads 27 tocorresponding contacts 54 on the first interconnect device 51. Thesecond interconnect device 52 is similarly mounted to the second surface16B of the second substrate 14 generally over the opening 16D and thethird semiconductor device 24 is similarly coupled to the secondinterconnect device 52. The substrates 14, 16, 18 are positioned withrespect to the base substrate 12 and with respect to each other so thatthe semiconductor devices 20, 22, 24 are positioned generally withinrespective openings 14D, 16D and 18D. The first and second interconnectdevices 51, 52 therefore provide a structural interface and anelectrical interface for mounting the semiconductor devices 22, 24 overthe openings 14D and 16D, respectively. Accordingly, the overall heightof the semiconductor structure 10 is reduced and the length of thesignal paths between successive semiconductive devices is shortercompared to the prior art.

Referring now to FIGS. 5 and 6, with like reference numeralscorresponding to like elements, the semiconductor structure 10 is shownaccording to a third embodiment of the present invention. In thisembodiment, a third interconnect device 53 is shown with interconnectdevices 51, 52 mounted to corresponding first surfaces 14A, 16A, 18Agenerally over respective openings 14D, 16D, 18D. In the illustratedembodiment of FIG. 5, the interconnect devices 51, 52, 53 function toprovide a structural interface for the semiconductor devices 20, 22, 24,respectively. The interconnect devices 51, 52, 53 may comprise a flexcircuit without any conductive wires, and thus, is non-conductive, or aflex circuit in which there is no electrical connection with theconductive wires. The interconnect devices 51, 52, 53 are coupled to thesubstrates 14, 16, 18, respectively, using an appropriate adhesive 60 orother suitable fastening means.

The semiconductor devices 14, 16, 18 are mounted on the interconnectdevices 51, 52, 53, respectively, using an appropriate adhesive 62 orother suitable semiconductor fastening means, such that thesemiconductor devices 14, 16, 18 are positioned within respectiveopenings 14D, 16D, 18D of the respective substrates 14, 16, 18. Thus, inthis embodiment, the semiconductor devices 20, 22, 24 are positionedgenerally within respective substrates 14, 16, 18 while in the secondembodiment the semiconductor devices 22, 24 are positioned overrespective substrates 14, 16. The semiconductor devices 14, 16, 18 areelectrically coupled to respective substrates 51, 52, 53 using bondwires 58 coupling portions of respective second plurality of substratebond pads 42, 44, 46 to respective plurality of semiconductor devicebond pads 26, 27, 28. It will be appreciated by those skilled in the artthat the backsides 20B, 22B, 24B of the semiconductor devices 20, 22, 24may be electrically coupled to respective interconnect devices 51, 52,53 by electrically coupling a portion of the contacts 54, 56 on theinterconnect devices 51, 52, 53 to respective first plurality substratebond pads 36, 38, 40 and another portion of the contacts 54, 56 to thebacksides of the semiconductor devices 20, 22, 24.

In the illustrated embodiment of FIG. 6, the interconnect devices 51,52, 53 are electrically and physically coupled to respective substrates14, 16, 18 as a portion of the contacts 54, 56, 57 (with referencenumeral 57 representing contacts in the third interconnect device 53)are coupled to corresponding respective first plurality substrate bondpads 36, 38, 40. It will be appreciated by those skilled in the art thatthe interconnect device 51, 52, 53 may be physically secured to therespective substrates 14, 16, 18 using an appropriate adhesive, in placeof or in addition to the physical coupling provided by the contacts 54,56, 57 and the bond pads 36, 38, 40. The semiconductor devices 20, 22,24 are also electrically and physically coupled to respectiveinterconnect devices 51, 52, 53 as respective semiconductor bond pads26, 27, 28 are coupled to portions of respective contacts 54, 56, 57 ofthe interconnect devices 51, 52, 53 using the solder balls 48, 49, 50.The interconnect devices 51, 52, 53 therefore provide a structuralinterface and an electrical interface for mounting the semiconductordevices 20, 22, 24 generally within the openings 14D, 16D, 18D,respectively. The overall height of the semiconductor structure 10 isagain reduced and the length of the signal paths between successivesemiconductive devices is also shorter as compared to the prior art.

As the semiconductor devices 20, 22, 24 are positioned generally withincavities or openings formed in the substrates, the semiconductor devices20, 22, 24 may be aligned so that a center of the semiconductor devicesintersect a line which is substantially perpendicular to the basesubstrate 12 and the other substrates 14, 16, 18. However, it should beapparent that the semiconductor devices 20, 22, 24, from one substrateto another, may be aligned as required for a particular application. Thesemiconductor devices 20, 22, 24 may therefore be offset with respect toeach other. Similarly, the substrates 14, 16, 18 may be aligned togetheror offset from each other.

It is to be understood that the embodiments of the present invention areillustrative only, as the number of substrates and semiconductor devicesmay vary depending on the particular application. It will be appreciatedby those skilled in the art that each of the substrates may include aplurality of cavities or openings along with a requisite number ofinterconnect devices, as appropriate, to accommodate a desired number ofsemiconductor devices. The semiconductor devices, and hence, thecavities or openings may be formed in a uniform or non-uniform patternas required for a particular application. It will be further appreciatedby those skilled in the art that a plurality of substrates may bemounted on the base substrate 12 or on each other as required for aparticular application. It should be apparent that the substrates may beconfigured to support semiconductor devices of varying types and sizessuch that there is no restriction to the types and sizes ofsemiconductor devices that may be used. Further, the semiconductorstructure 10 may be configured as a hybrid of two or more of theembodiments disclosed in the present invention.

Having described the invention in detail and by reference to preferredembodiments thereof, it will be apparent that modifications andvariations are possible without departing from the scope of theinvention defined in the appended claims.

What is claimed is:
 1. A method of manufacturing a semiconductorstructure comprising the steps of: providing a base substrate having afirst surface; forming a first plurality of base substrate bond pads onsaid first surface of said base substrate; providing a first substratehaving a first surface, a second surface, and at least one cavity formedwithin said first surface of said first substrate; forming a firstplurality of first substrate bond pads on said first surface of saidfirst substrate; providing at least one semiconductor device having aplurality of semiconductor device bond pads; coupling at least one ofsaid plurality of semiconductor device bond pads to at least one of saidfirst plurality of base substrate bond pads; positioning said firstsubstrate over said first surface of said base substrate such that saidsemiconductor device is generally within said at least one cavity; andcoupling at least one of said first plurality of first substrate bondpads to at least one of said first plurality of base substrate bondpads.
 2. The method of claim 1, further comprising the steps of: forminga second plurality of first substrate bond pads on said second surfaceof said first substrate; providing a second semiconductor device havinga plurality of second semiconductor device bond pads; and, coupling atleast one of said plurality of second semiconductor device bond pads toat least one of said second plurality of first substrate bond pads. 3.The method of claim 1, wherein said step of coupling at least one ofsaid plurality of semiconductor device bond pads to at least one of saidfirst plurality of base substrate bond pads comprises the step ofelectrically and physically coupling said at least one semiconductordevice to said base substrate using solder balls to couple at least oneof said plurality of semiconductor device bond pads to at least one ofsaid first plurality of base substrate bond pads.
 4. The method of claim1, wherein said step of coupling at least one of said first plurality offirst substrate bond pads to at least one of said first plurality ofbase substrate bond pads comprises the step of electrically andphysically coupling said first substrate to said base substrate usingsolder balls to couple at least one of said first plurality of firstsubstrate bond pads at least one of said first plurality of basesubstrate bond pads.
 5. A method of manufacturing a semiconductorstructure comprising the steps of: providing a first substrate having atleast one opening; forming a plurality of first substrate bond pads on asurface of said first substrate; providing an interconnect device;coupling said interconnect device to said first substrate generally oversaid at least one opening; providing at least one semiconductor devicehaving a plurality of semiconductor device bond pads; and coupling saidat least one semiconductor device to said interconnect device generallyover said at least one opening.
 6. The method of claim 5, wherein saidstep of coupling said at least one semiconductor device to saidinterconnect device generally over said at least one opening comprisesthe step of electrically and physically coupling said at least onesemiconductor device to said interconnect device using solder ballscoupling at least one of said plurality of semiconductor device bondpads to at least one of said plurality of first substrate bond pads. 7.The method of claim 6, wherein said interconnect device comprises a flexcircuit.
 8. The method of claim 5, wherein said step of coupling said atleast one semiconductor device to said interconnect device generallyover said at least one opening comprises the step of electrically andphysically coupling said at least one semiconductor device to saidinterconnect device using TAB tape.
 9. A method of manufacturing asemiconductor structure comprising the steps of: providing a firstsubstrate having at least one opening; forming a plurality of firstsubstrate bond pads on a surface of said first substrate; providing aninterconnect device; coupling said interconnect device to said firstsubstrate generally over said at least one opening; providing at leastone semiconductor device having a plurality of semiconductor device bondpads; and coupling said at least one semiconductor device to saidinterconnect device generally within said at least one opening.
 10. Themethod of claim 9, wherein said interconnect device comprises aplurality of interconnect device contacts, and wherein said step ofcoupling said interconnect device to said first substrate generally oversaid at least one opening comprises the step of electrically andphysically coupling said interconnect device to said first surface ofsaid first substrate with at least one of said plurality of interconnectdevice contacts being electrically coupled to at least one saidplurality of first substrate bond pads.
 11. The method of claim 10,wherein said step of coupling said at least one semiconductor device tosaid interconnect device generally within said at least one openingcomprises the step of physically and electrically coupling said at leastone semiconductor device to said interconnect device using solder ballscoupling at least one of said plurality of first semiconductor devicebond pads to at least one of said plurality of first interconnect devicecontacts.
 12. The method of claim 9, wherein said interconnect device isphysically but not electrically coupled to said first surface of saidfirst substrate.
 13. The method of claim 12, wherein said step ofcoupling said interconnect device to said first substrate generally oversaid at least one opening comprises the step of coupling saidinterconnect device to another surface of said first substrate.
 14. Themethod of claim 13, further comprising the step of electrically couplingat least one said plurality of semiconductor bond pads to at least oneof said plurality of first substrate bond pads using a bond wire. 15.The method of claim 9, wherein said plurality of semiconductor devicebond pads are positioned on a frontside of said first semiconductordevice, and wherein said step of coupling said at least onesemiconductor device to said interconnect device generally within saidat least one opening comprises the step of electrically coupling abackside of said at least one semiconductor device to said firstinterconnect device, and further comprising the step of electricallycoupling at least one said plurality of semiconductor bonds to at leastone of said plurality of first substrate bond pads using a bond wire.16. A method of manufacturing a semiconductor structure according toclaim 5, wherein said interconnect device is coupled to said substrategenerally over said at least one opening by positioning saidinterconnect device on top of said first substrate and generally oversaid at least one opening.
 17. A method of manufacturing a semiconductorstructure according to claim 5, wherein said interconnect device iscoupled to said substrate generally over said at least one opening bypositioning said interconnect device underneath said first substrate andgenerally over said at least one opening.
 18. A method of manufacturinga semiconductor structure according to claim 5, further comprising:providing a base substrate having a first surface; forming a firstplurality of base substrate bond pads on said first surface of said basesubstrate; and, coupling at least one of said plurality of firstsubstrate bond pads to at least one of said first plurality of basesubstrate bond pads such that said interconnect device lies between saidsemiconductor device and said base substrate.
 19. A method ofmanufacturing a semiconductor structure according to claim 9, whereinsaid interconnect device is coupled to said substrate generally oversaid at least one opening by positioning said interconnect device on topof said first substrate and generally over said at least one opening.20. A method of manufacturing a semiconductor structure according toclaim 9, wherein said interconnect device is coupled to said substrategenerally over said at least one opening by positioning saidinterconnect device underneath said first substrate and generally oversaid at least one opening.
 21. A method of manufacturing a semiconductorstructure according to claim 9, further comprising: providing a basesubstrate having a first surface; forming a first plurality of basesubstrate bond pads on said first surface of said base substrate; and,coupling at least one of said plurality of first substrate bond pads toat least one of said first plurality of base substrate bond pads suchthat said interconnect device lies between said semiconductor device andsaid base substrate.